Process for fabricating threaded elements from the age-hardenable alloys

ABSTRACT

Threaded elements having improved mechanical properties for high-temperature service are fabricated from the age-hardenable superalloys in a process comprising: solution heat treating the alloy and establishing a grain size corresponding to ASTM 2-6, or more preferably ASTM 4-5; forming the threads; stabilization heat treating the threaded alloy; and aging.

United States Patent Inventors Marvin C. Vanwanderhnm;

John A. Harris, Jr., Palm Beach, Fla.; James J. Campbell, Cincinnati,Ohio 811,201

Mar. 27, 1969 Oct. 26, 1971 United Aircraft Corporation East Hartford,Conn.

Appl. No. Filed Patented Assignee PROCESS FOR FABRICATING THREADEDELEMENTS FROM THE AGE-HARDENABLE ALLOYS 6 Claims, No Drawings U.S. Cl.l48/l2.7, 148/1 2.3 Int. Cl C221 1/00, C22f 1/10, C2ld 9/00 Fieldol'Search 148/12.3, 11.5, 12.7

[56] References Cited UNITED STATES PATENTS 2,637,672 5/1953 Losco eta1. 148/12.3 2,957,790 10/1960 Metcalfe 148/1 2.3 3,357,868 12/1967Tanczyn.... 148/12.3 3,376,780 4/1968 Tanczyn 148/12.3

Primary Examiner-L. Dewayne Rutledge Assistant Examiner-W. W. StallardAttorney-Richard N. James BACKGROUND OF THE INVENTION The presentinvention relates to the production of threaded elements from theage-hardenable superalloys.

1n gas turbine engines, a number of threaded elements, such as bolts andcompressor tie rods, are utilized in environments involving exposureunder stress to elevated temperatures. As manufactured by conventionaltechniques, these elements are prone to failure with time, due primarilyto poor stress relaxation resistance and insufficient thread strength.

Two alloys, Waspaloy and Astroloy, are widely used in applications ofthis nature, although other age-hardcnable alloys such as lnco 901,lnconel x 750 and Udimet 700, are also available for this type ofservice. Waspaloy, which is suitable for this type of service up totemperatures of about 1,200 F. has the following nominal composition byweight: 19.5% Cr, 13.5% Co, 0.07% C, 3% Ti, 1.4% A1, 4% Mo, 0.005% B,0.08% Zr, bal. Ni. For service over 1,200 F., Astroloy is commonly usedat a nominal composition, by weight of: 15.5% Cr, 17% Co, 0.07%C, 3.3%Ti, 4.5% a], 5.3% Mo, 0.03% B, bal. Ni.

The conventional threading practice involves rolling of the threads inbarstock after the stablization heat treatment but prior to aging.Threaded elements so formed, however, exhibit poor stress relaxation andthread failure resistance and, hence, are prone to thread failure inservice.

SUMMARY OF THE INVENTION The present invention describes a fabricationtechnique for providing threaded elements from the age-hardenable alloyscharacterized by improved mechanical properties in elevated temperatureapplications.

The improved properties are achieved by first establishing a grain sizeof ASTM 2-6 by appropriate heat treatment and, then, by altering theconventional thread forming procedure to provide rolling of the threadsprior to stabilization and aging. The process thus involves:

solution heat treating the alloy to establish a grain size of ASTM 2-6or more preferably ASTM 4-5; forming the threads; stabilizing heattreating the threaded alloy; and aging.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For service to temperatures upto about 1,200 F., suitable stock is formed from an alloy consisting of,by weight,: 18-21 percent chromium, 12-15 percent cobalt, 0.04-0.10percent carbon, 3.5- percent molybdenum, 2.75-3.25 percent titanium,1.2-1.6 percent aluminum, 0.02-0.08 percent zirconium, 0.003-0.01percent boron, balance essentially nickel. The stock is solution heattreated at a temperature of about 1 ,825-l ,900 F. for 2-4 hours andcooled at a rate equivalent to air cool or faster the conditions beingselected to establish a grain size of ASTM 2-6, preferably ASTM 4-5. Anymachining of boltheads, etc., may be done either before or after thesolution heat treatment. Threads are formed by a single rolling process.After thread rolling, the parts are stabilization heat treated byheating to about 1,550 F; holding at heat for about 4 hours; and coolingin air. After stabilization, the parts are precipitation heat treated byheating to about 1,400 F.; holding at heat for about 16 hours; andcooling in air.

For service in excess of about 1,200 F., the stock is formed from apreferred composition consisting of, by weight: 14-16 percent chromium,16-18 percent cobalt, 0.03-0.09 percent carbon, 4.5-5.5 percentmolybdenum, 3.35-3.65percent titanium 3.85-4.15 percent aluminum,002-003 percent boron, balance essentially nickel. The stock is solutionheat treated at a temperature of 1,975 F. or higher; held at temperatureto establish a grain size corresponding to ASTM 2-6, preferably 4-5; andcooled at a rate equivalent to air cool or faster. Threads are formed ina single rolling process. After thread rolling, parts are stabilizingheat treated by: holding the part at a temperature of about 1,600 F.,for about 8 hours; and cooling at a rate equivalent to aircooling. Theparts are subsequently precipitation heat treated at about 1,200 F. for24 hours and air cooled; and heat treated at about 1,400 F. for about 8hours and air cooled.

A number of specimens were prepared with varying heat treatments asaffecting grain size and were subjected to a variety of tests comparingthe effect of both grain size and the processing sequence. The resultsof a number of these tests are summarized in the following tables.

TABLE I Specimen Grain Size/Threading Practice Room Temperature TensileResults and Specimen Data CKB Grain YS, UTS, EL, RA, Failure Part Size Ks.i. K s.i. k '2 Location Number Range 9561 Coarse 133 210 21 16 Threads130 208 21 I9 Shank 123 180 15 13 Shank 9562 Coarse I25 192 ll 16 Shank122 188 II 16 Shank 121 I83 l8 l6 Shank 9563 Coarse 160 10 9 Threads 122163 I0 9 Threads I65 8 8 Threads 9564 Coarse 119 179 17 14 Threads 122I77 l5 12 Threads 126 168 I5 13 Threads 9565 Coarse 121 178 15 11Threads 129 191 l7 13 Threads 127 180 14 11 Thread: 9571 Fine 141 208 2529 Shank 141 215 24 27 Shank 143 216 24 J1 Shank 9572 Fine 141 214 25 J2Shank 149 223 23 2! Shank 156 220 24 51 Shank 9573 Fine I49 200 I2 9Threads 153 201 ll 9 Threads 162 209 ll 9 Thread: 9574 Fine 151 206 1415 Threads 157 218 22 27 Shank 160 224 23 3| Shank 9575 Fine 158 221 1615 Threads 148 214 16 12 Threads 224 24 32 Shank TABLE III l,400 F.Tensile Results and Specimen Data CKB Grain YS, UTS, EL, RA. Failurepart Size K s.| K a.i. k L gi Number Range 956I Coarse l I 8 154 I I9Shank I17 I51 22 34 Shank I20 160 l9 2! Shank 9562 Coarse I08 I46 13 $3Shank I08 I48 28 36 Shank I I8 154 26 30 Shank 9563 Coarse I I4 147 1831 Shank I08 I49 21 32 Shank I07 I51 26 32 Shank 9564 Coarse I I6 154 2126 Shank I06 I50 24 30 Shank I07 I50 23 25 Shank 9565 Coarse I I7 I54 2225 Shank I07 150 21 29 Shank I l I 153 24 24 Shank 957l Fine I22 I52 16I6 Shank I30 I50 I3 19 Shank I30 157 l1 l5 Shank 9572 Fine I28 I55 21 52Shank I28 I49 23 55 Shank I38 154 29 54 Shank 9573 Fine 136 I50 34 58Shank I40 I51 23 53 Shank I59 I69 30 52 Shank 9574 Fine I32 26 55 ShankI3I 147 23 S9 Shank 142 141 :9 s7 Shank 9575 Fine I32 l5] l0 14 Threadsl 32 149 I4 Threads I37 154 31 57 Shank TABLE IV I400 Fl85l0 ksi stressrupture results and specimen data Root Radius, Area Ratio. in.(Thousandths) CKB Grain El, RA;

part size Life, perper- Failure End End End End number range hr centcent location One Two One Two 9561 Coarse 50 8 8 Threads 93 93 8 8 58 2124 Threads 93 93 8 8 43 9 l2 Shank 93 93 8 8 62 l4 l4 Shank 93 93 8 89562 Coarse 44 I6 24 Shank 93 93 8 K 50 I9 Shank 93 93 8 8 57 25 26Shank 93 93 8 8 S3 23 29 Shank 93 93 8 8 9563 Coarse 40 I6 27 Shank 9393 I0 IO SI I3 20 Shank 93 92 l0 I0 52 I8 I9 Shank 92 92 l0 IO 69 l4 l5Shank 92 92 l0 I0 9564 Coarse 68 14 I6 Shank 93 93 l0 I0 48 I9 25 Shank92 92 l0 ll) 52 I6 22 Shank 93 93 l0 l0 6] I7 l8 Shank 92 92 10 I0 9565Coarse 54 I5 20 Shank 95 95 5 5 45 I9 23 Shank 95 95 5 6 62 l5 l7 Shank95 95 5 5 53 I7 22 Shank 95 95 5 6 9571 Fine I3 3 3 Threads 93 93 9 9 86 8 Shank 92 92 8 8 I5 I 1 Threads 92 92 9 9 l9 3 3 Threads 92 92 9 99572 Fine 29 41 64 Shank 92 93 8 8 34 37 5] Shank 92 92 8 S l i 3| 42 51Shank 92 92 8 8 9573 Fine 22 35 55 Shank 93 93 l0 I0 36 28 48 Shank 9292 I0 10 39 34 52 Shank 92 92 l0 l0 I6 45 58 Shank 93 93 I0 10 9574 Fine20 37 51 Shank 92 93 l0 I0 22 53 65 Shank 92 93 l0 I0 45 60 Shank 92 9210 H) I8 42 7O Shank 92 92 I0 I0 9575 Fine 63 29 44 Shank 95 95 7 6 3036 60 Shank 96 95 7 6 44 48 Shank 96 96 6 5 47 45 55 Shank 96 96 5 6TABLE V l,300 F./65.0 K s.i./I 00 hr. Stress Relaxation Results andSpecimen Data CKB Grain Part Size Relaxation. Number Range 1:

956l Coarse 4 7 9562 Coarse 3 8 9563 Coarse 2 6 9564 Coarse 3 9 9565Coarse 3 0 7I Fine 6 I0 9572 Fine l2 8 9573 Fine I3 I2 9574 Fine 14 99575 Fine I0 TABLE VI Relative Influence of Grain Size on MechanicalProperties D Detrimental Influence B Beneficial Influence N No InfluenceThe results confirm that both grain size and threading practice exert aninfluence on mechanical properties. The finergrained specimens producedresults equal or superior to the coarser-grained specimens in tenns ofall mechanical properties except stress rupture life and stressrelaxation resistance. Unfortunately, the influence on grain size can beseen to exert contradictory effects in terms of the physical propertiesrequired of a threaded element. The choice of a grain size of ASTM 2-6or more preferably ASTM 4-5 represents the best compromise for threadedelements, recognizing also the problems of precise grain size control inproduction processes.

Basically, the solution-roll-stabilize-age threading sequence improvesthe ability of the threads to resist stress relaxation and failure. Itmust, however, be considered in combination with the selection of therequired grain size for optimum results. Clearly, the program hasdemonstrated that, as opposed to conventional processing techniques, theimproved process described herein may be utilized to provide threadedelements which are not susceptible to thread failure.

While the invention has been described in connection with certainexamples and preferred embodiments, these are illustrative only. It willbe understood that the invention is not to be limited to the exactdetails described, for obvious modifications will occur to those skilledin the art.

We claim:

I. The process of fabricating threaded elements from the age-hardenablealloys which comprises:

forming the threads on solution heat treated, age-hardenable alloy stockhaving a grain size corresponding to about ASTM 2-6;

subjecting the threaded alloy to a stabilization heat treatment; and

aging the alloy.

2. The process of fabricating threaded elements from the age-hardenablenickel-base alloy which comprises:

solution heat treating the alloy to establish a grain size substantiallycorresponding to ASTM 2-6;

rolling the threads; subjecting the threaded alloy to a stabilizationheat treatment and precipitation heat treating the stabilized alloy. 3.The method of fabricating threaded elements for service up to aboutl,200 F. which comprises:

providing suitable stock from an alloy consisting essentially of, byweight, about l8-2l percent chromium, 12-] 5 percent cobalt, 3.5-5percent molybdenum, 2.75-3.25 percent titanium, 1.2-1.6 percentaluminum, about 0.07 percent carbon, about 0.005 percent boron, about0.08 percent zirconium, balance nickel; solution heat treating the alloyat l,800-l,900 F. for a minimum of about 2 hours and establishing agrain size corresponding to about ASTM 2-6; rolling the threads in thestock after cooling; stabilization heat treating the alloy; andprecipitation heat treating the alloy at about l,400 F. 4. The processaccording to claim 3 wherein: the stabilization heat treatment isconducted at a temperature of about l,500 F. 5. The method offabricating threaded elements for hightemperature service whichcomprises:

providing suitable stock from an alloy consisting essentially of, byweight, 14-16 percent chromium, 16-18 percent cobalt, 4.5-5.5 percentmolybdenum, 3.35-3.65 percent titanium, 3.85-4.l5 percent aluminum,about 0.06 percent carbon, about 0.03 percent boron, balance nickel;solution heat treating the alloy at a temperature of at least l,975 F.and establishing a grain size corresponding to about ASTM 2-6; rollingthe threads in the stock after cooling; stabilization heat treating thealloy; and precipitation heat treating the alloy at about l,200 F. 6.The process according to claim 5 wherein: the stabilization heattreatment is conducted at a temperature of about l,600 F.

22 13? UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3,615,906Dated October 26, 1971 Patent No.

Inventor) Marvin C. Vanwanderham et a1 It 15 certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

Claim 3, column 6, line 13 1800 should read -l82S-- Claim 4, column 6,line 21 l500 should read --l550-- Signed and sealed this 28th day ofMarch 1972.

(SEAL) Attest:

EDWARD M.FLETCHI ]R, JR. ROBERT GOT'ISCHALK Commissioner of PatentsAttesting Officer

2. The process of fabricating threaded elements from the age-hardenablenickel-base alloys which comprises: solution heat treating the alloy toestablish a grain size substantially corresponding to ASTM 2- 6; rollingthe threads; subjecting the threaded alloy to a stabilization heattreatment; and precipitation heat treating the stabilized alloy.
 3. Themethod of fabricating threaded elements for service up to about 1,200*F. which comprises: providing suitable stock from an alloy consistingessentially of, by weight, about 18-21 percent chromium, 12-15 percentcobalt, 3.5-5 percent molybdenum, 2.75-3.25 percent titanium, 1.2-1.6percent aluminum, about 0.07 percent carbon, about 0.005 percent boron,about 0.08 percent zirconium, balance nickel; solution heat treating thealloy at 1,800*-1,900* F. for a minimum of about 2 hours andestablishing a grain size corresponding to about ASTM 2-6; rolling thethreads in the stock after cooling; stabilization heat treating thealloy; and precipitation heat treating the alloy at about 1,400* F. 4.The process according to claim 3 wherein: the stabilization heattreatment is conducted at a temperature of about 1,550* F.
 5. The methodof fabricating threaded elements for high-temperature service whichcomprises: providing suitable stock from an alloy consisting essentiallyof, by weight, 14-16 percent chromium, 16-18 percent cobalt, 4.5-5.5percent molybdenum, 3.35-3.65 percent titanium, 3.85-4.15 percentaluminum, about 0.06 percent carbon, about 0.03 percent boron, balancenickel; solution heat treating the alloy at a temperature of at least 1,975* F. and establishing a grain size corresponding to about ASTM 2-6;rolling the threads in the stock after cooling; stabilization heattreating the alloy; and precipitation heat treating the alloy at about1,200* F.
 6. The process according to claim 5 wherein: the stabilizationheat treatment is conducted at a temperature of about 1,600* F.